In buildings having pipes made of plastic there is a danger that, in case of fire in a particular room, the pipe system will quickly melt and burn, whereupon both fire and smoke can move through the resulting openings in walls and floors to adjacent rooms.
To prevent this from happening, it has been proposed, e.g., in Swiss Pat. No. 566,513, to surround the pipes at the point of passage through walls or floors with protective casings containing an insert, e.g., acqueous potassium silicate or sodium silicate, which is caused by the developing heat to foam up and to seal the passages. This type of insert has a rather large overall height and is particularly useful where the fire in a particular room is extremely hot. However, in the case of fires developing a lesser amount of heat, such as smouldering fires, it takes a certain length of time for the insert to complete its foaming action and to seal the wall or floor passage.